Despite the fundamental nature of reproduction, for many it is a process fraught with frustration, inefficiency and imperfections. Infertility affects 10 to 15 percent of couples attempting to conceive. Among all women who conceive, the incidence of spontaneous miscarriage has been estimated at between 15 and 31 percent, and in many cases the cause is unknown. Additionally, of the four million infants born each year in the United States, between eight and 15 percent will be born prematurely and as a result, will experience higher morbidity and mortality, compared with full-term infants. . An intervention with even a small relative effect on preventing the occurrence of any of these adverse outcomes has great implications at the population level because of the large potential attributable benefit. For this reason, the Epidemiology Branch of DESPR Intramural research at the NICHD is conducting a multi-site randomized trial to evaluate the effect of daily low-dose aspirin and folic acid, compared folic acid and placebo alone, on reproduction at all phases, beginning at preconception and continuing throughout pregnancy. The trial will assess the effects of aspirin on each of the phases, including implantation and live birth. The trial has the goal of recruiting and completing the intervention in a sample of at least 1,600 women, age 18-40, who have previously experienced one or two pregnancy losses and who are actively trying to conceive.